Tooth pulp afferents are known to project to nucleus caudalis, (in addition to other regions of the trigeminal nucleus), a region believed to play a major role in pain processing of oral-facial stimuli. However, many questions concerning the processing and relay of tooth pulp input with the nucleus still remain unanswered. It is the aim of this project to study the distribution of tooth pulp afferents to the nucleus caudalis, the responses of neurons in the nucleus to tooth pulp stimulation and the projection targets of these nuerons. The interaction and covergence of tooth pulp input with activity arising from skin and other brain regions will also be investigated in order to determine what modulatory mechanisms exist. The experiments will involve standard electrophysiological recording techniques in anaesthetized cats. Glass-coated tungsten microelectrodes will be used to record from neurons in the superficial layers of the nucleus. Stimulating electrodes will be placed in tooth pulps, infraorbital nerve, thalamus, periaqueductal gray, nucleus raphe magnus and skin in order to determine the interaction of other regions and the the projection site of the neurons. The results of this study will help explain the neurophysiological basis of dental pain as well as other pains such as trigeminal neuralgia for which tooth pulp input may share a common path or at least serve as a useful model. These studies may also provide new insights into, and possible improvements of, the recent methods of transcutaneous nerve stimulation and brain stimulation produced analgesia being used to treat some pain conditions.